1. Field of the Invention
This invention relates to a flexible web guide. More particularly, the invention is a hydrodynamic tape guide including a thin metal foil attached to a substrate by a pin inserted into a groove in the substrate.
2. Description of the Related Art
Web and tape guiding apparatus are well known. A common use of such an apparatus is for guiding data tapes in magnetic or optical data tape drives over a read and/or write head. Guiding of the tape over the head is critical to the writing of data to and the reading of data from the tape. A typical magnetic tape drive includes several elements in the tape path to ensure proper alignment and operation of the tape and head. For example, the tape paths of the IBM 3480/3490 Magnetic Tape Subsystems include a supply reel inside a tape cartridge, a vibration decoupler, a cleaner blade, an arcuate supply side air bearing device, a magnetic read/write head, an arcuate storage side air bearing device, a tension transducer, a storage reel, and tape edge guides along the sides of the bearing surfaces. The tape edge guides are located along the arcuate bearing surfaces because the tape in such proximity can support a larger guiding force without collapsing than can freely suspended tape. The tape edge guides physically align the lateral position (i.e. in the direction of the tape width) of the tape relative to the read/write head. Lateral positioning maintains proper alignment between the read/write elements of the head and the data tracks on the magnetic tape. The tape guides also support and guide the tape in its easy direction of bending (i.e. in the direction of tape travel).
Guides for easy direction tape guiding may be pneumatic or hydrodynamic. A pneumatic tape guide includes an externally pressurized air bearing, as in the IBM 3480/3490 Magnetic Tape Subsystems. Although an air bearing can dramatically reduce tape friction and stiction, it is expensive to implement. An air bearing is expensive because it requires the space and parts for air to be provided under controlled pressure. A very expensive and acoustically noisy air pump must be provided to supply the necessary air flow and regulate air pressure to the air bearing. In the IBM 3480/3490 Magnetic Tape Subsystem, the air bearing surface is created by drilling large, solid metal bearings. Another known air bearing has attempted to reduce manufacturing costs by attaching a metal foil to a bearing block. Bareman et al, Air Bearing, IBM Technical Disclosure Bulletin, Vol. 24, No. 12, May, 1982, pp. 6603-6604. Unfortunately, the foil is attached to the block with screws which could tear, stretch, or otherwise damage the foil. Another air bearing includes a perforated metal foil adhesively attached to a substrate, as disclosed in commonly assigned, copending U.S. patent application Ser. No. 07/902.243, filed Jun. 22, 1992. Modern magnetic tape subsystems are growing increasingly smaller and, unfortunately, reducing the space available therein for an air pump.
Hydrodynamic, or non-pneumatic, tape guides do not include supplied air. Instead, these tape guides operate on the theory that a film of air forms between a tape and the tape guide when the tape is in motion, thereby reducing friction and wear. Two basic types of hydrodynamic tape guides are known. The first such guide is a fixed post. A fixed post is simple to implement, but suffers from stiction between the tape and the post when the tape is at rest and high impact friction during start/stop of tape motion. A second hydrodynamic tape guide is a roller. Compared to a fixed post, a roller reduces friction when the tape is in motion and reduces stiction when the tape is at rest. However, a roller introduces a source of vibration into the tape path which may disrupt the head-tape interface. A roller stores energy that must be positively controlled to maintain adequate closed loop tape tension, and steers tape differently than does a fixed post, often requiring grooves or other geometries to prevent the tape from flying too far away therefrom.
A hydrodynamic hybrid of a fixed post and roller is disclosed in commonly assigned, copending U.S. patent application Ser. No. 07/714,965, filed Jun. 13, 1991. Such application discloses a constrained pivot compound radius guide post mounted on an axle which allows it to pivot when the tape changes direction, thereby reducing startup stiction. Above a certain rotation angle the post is prevented from further rotation. The compound radius longitudinal contour reduces friction by maximizing the thickness of the air film between the tape and the post.
Hydrodynamic tape guides require a smooth and continuous tape bearing surface. In addition, the tape bearing surface must be electrically conductive to minimize static charge. Such bearing surfaces are known to be manufactured by machining, grinding, and/or lapping a block or cylinder of metal. Though less complex than air bearings, such manufacturing is still relatively expensive, particularly in modern low cost tape drives. Cast metal bearing surfaces are inexpensive, but are not sufficiently smooth for high speed tape drives. Molded plastic bearing surfaces are smoother, but not as smooth as lapped metal surfaces, and dimensional tolerances are not easily controlled particularly to generate a compound radius contour, if desired. Metal plated plastic bearing surfaces still further improve the smoothness, but increase the complexity and cost of manufacture.
A hydrodynamic tape guide employing a metal foil to reduce cost is disclosed in European Patent Application 0217157. Unfortunately, the techniques for attaching such metal foil to a substrate are inadequate. Adhesives are difficult to work with, and may fail during use. Simple resilient wrapping of the foil about the substrate is still more likely to fail during use. In addition, the foil is attached to the substrate with the ends overlapped, which can result in surface disruptions which interfere with tape travel, or which concentrate stress and result in failure of the metal foil. Other techniques for attaching a thin sleeve to a contoured substrate are known, but suffer from similar problems.